The present invention relates to a method and to a device for conditioning a rock, sediment or soil sample in order to determine, by pyrolysis, at least one pollution characteristic of a natural soil potentially or really contaminated by polluting products, notably hydrocarbons and/or derivatives. The invention also allows analysis of pure polluting products, tars, bitumens, etc., for example.
For better comprehension, it can be reminded that:
during an accidental or chronic discharge (for example pipeline breakage, loss of tightness of a storage means, a tank for example, or after abandonment of ancient industrial sites), a certain amount of hydrocarbon compounds can seep into the soil, which causes pollution of all or part of said soil,
knowledge of the type of pollutant (gasoline, kerosine, gas oil, lubricant, tars, bitumen, chlorine derivatives, . . . ) and knowledge of the extension in time and in space of the pollution is of great importance to people in charge of diagnosis, environmental impact studies and remediation of polluted soils. It is in fact well-known that the remediation techniques used depend on the type of polluting products.
It is therefore very important to quickly determine the nature of the pollutants and the quantity of soil to be treated, which directly depends on the extension of the pollution, at depth as well as at the surface. Determination of the degree of pollution of a soil allows to evaluate the volumes of ground to be treated, to determine the most suitable treating methods and the costs corresponding to the implementation thereof.
It then appears that systematic analysis of potentially or really polluted soil samples allows to quickly make a diagnosis concerning the nature and the extension of the pollution and the associated main risks (water table contamination for example).
In order to obtain reliable qualitative and/or quantitative analyses, it is generally necessary to subject samples of pure polluting products to pyrolysis.
Knowledge of such information allows to optimize operations of remediation of contaminated sites from the diagnosis stage. Without being totally suppressed, long and costly laboratory analyses are limited to the required minimum completing the information systematically collected by means of the method according to the present invention.
The ROCK-EVAL technique developed by the claimant, which is notably described in documents U.S. Pat. Nos. 4,153,415; 4,229,181; 4,352,673; 4,519,983, and in French patent application FR-94/08,383, is well-known. This method, which is fast, practically automatic, has been developed for characterization of mother rocks or reservoir rocks and of the hydrocarbons contained therein.
However, this method and the device are not totally suited for precise characterization of the various hydrocarbon cuts that can be contained in soils polluted by such products.
Document FR-2,753,271 describes an improvement of the ROCK-EVAL technique allowing more precise characterization of the pollutants, notably hydrocarbon and/or derivative type pollutants (chlorine, sulfur compounds, . . . ), contained in a polluted soil.
However, during analysis of polluted soils, the lighter polluting fractions, which can be related to gasoline and/or kero sine cuts with less than 12 carbon atoms, are very volatile. Although the baskets containing the sample to be analyzed can be inserted in a cooled sample changer, the volatile compound losses can exceed 90% in 24 hours. This is explained by the high vapour pressures of these light compounds and by the fact that the baskets containing the samples are not hermetically sealed.
The object of the present invention is consequently to limit or to suppress these evaporation losses, or to act on the evaporation rate.
The present invention thus relates to a device for conditioning a soil or rock sample polluted by hydrocarbons, or a hydrocarbon-based pollutant sample. The device comprises a receptacle containing the sample and a determined quantity of a material having the capacity to adsorb at least partly the hydrocarbons.
The sample can be surrounded in the receptacle by two adsorbent material layers.
The sample can be at least partly mixed with the adsorbent material.
The adsorbent product can consist of at least one of the following materials: silica, graphitized carbon, bentone, molecular sieve, clay.
The receptacle can comprise a bottom made of a gas porous material, a sintered metal for example.
The invention also relates to the method of analysis by pyrolysis of a soil or rock sample polluted by hydrocarbons, or of a hydrocarbon-based pollutant sample. This method uses the aforementioned device.